The invention relates to hoist apparatus, and more particularly to devices for limiting the rotation of a hoist drum beyond a desired position.
A conventional hoist apparatus includes a hoist drum, a motor for selectively rotating the drum, and a hoist rope wound around the drum such that the rope winds on to and off of the drum in response to rotation of the drum in opposite directions. Typically, the rope is a wire rope and the drum has a helical groove in which the rope is reeved as the rope winds on to the drum. A bottom block is supported by the rope such that the bottom block moves up and down as the rope winds on to and off of the drum.
In order to prevent a load or the bottom block from being raised too high, to prevent the rope from paying out too far (such that it could wrap around the drum the opposite way), or to prevent the load from being lowered too low, it is known to provide a limit switch for preventing the rope from being wound too far on to or off of the drum. Such a switch can be, for example, a geared limit switch. Other types of limit switches are disclosed in U.S. Pat. Nos. 3,850,380 and 5,405,027.